Herpes simplex virus type 1 (HSV-1) is ubiquitous in the human population and causes a variety of clinically significant acute diseases which can be life-threatening to immunocompromised individuals. HSV-1 also establishes life-long latent infections characterized by periodic reactivation, virus shedding and recurrent disease. The ability of the virus to establish latent infections which cannot be cured by the immune response or existing antiviral drugs is the reason that HSV-1 continues to be a significant human pathogen. In this proposal, three senior herpesvirologists will conduct a series of collaborative studies designed to elucidate the mechanism of establishment, maintenance and reactivation of HSV-1 latency by identifying the viral and cellular proteins and activities that result in latency and reactivation. Project 1 will focus on the state of viral chromatin during latent infection and will investigate the roles of ICPO and the latency-associated transcripts (LATs) in regulating the chromatization of latent genomes in collaboration with Projects 2 and 3. Project 1 will also examine the long-term immune response to HSV-1 and HSV-1 latent infection by defining the role of TLR2 signaling in the immune response. Project 2 will investigate the molecular and genetic mechanism by which clinical HSV-1 isolates become drug-resistant while retaining pathogenesis and permitting reactivation. In collaboration with Projects 1 and 3, Project 2 will also focus on how late gene expression is repressed by interferon gamma (IFN-y) and the LATs and later reactivated. Also in collaboration with Projects 1 and 3, Project 2 will examine the effects of IFN-y and newly discovered viral miRNAs on host gene expression. Project 3, in collaboration with Projects 1 and 2, will focus exclusively on the mechanisms of HSV-1, reactivation by attempting to identify the cellular proteins that mediate stress-induced reactivation, identifying the promoter elements in viral genes that respond to stress, and determining the effects of cdks on the activities of viral proteins induced by stress. Collectively, these studies will provide new insight into the mechanisms of HSV-1 latency and reactivation and define novel approaches to intervention in the HSV-1 life-cycle.